The present invention relates to steam property measuring devices and more particularly, to a device for measuring the quality of steam in a two-phase flow mixture.
The quality of a two-phase flow is a parameter of importance in the operation and design of heat exchangers, turbines, steam engines, pumps and piping systems. In heat exchangers that operate at saturated conditions, such as a steam generator of condenser, the performance is characterized by the state of fluid entering and leaving the heat exchanger. In order to quantify the state of the fluid at saturation conditions, the inlet or exit quality must be known. In a steam generator, for example, lower than expected outlet quality is an indication of poor heat transfer performance of inefficient steam separation equipment. In turbines, high moisture content at the turbine inlet can cause turbine blade erosion as well as reduced system efficiency.
A variety of techniques have been used for measuring the quality of steam. The throttling calorimeter, although in wide use, is subject to a number of constraints and problems. The accuracy is highly dependent on the flow conditions, and the probe is easily clogged with contaminants. The operating fluid is vented to the atmosphere, which makes it undesirable for use in harsh environments, such as nuclear power plants. Furthermore, the throttling calorimeter is not easily adapted for remote operation. Vibrating vane-type quality measuring devices alter the fluid state and thus may yield erroneous results. Techniques using chemical tracers, although reliable, require the addition of chemicals to the working fluid, which is unacceptable in systems that require high purity of the steam. Such techniques are not adaptable to remote operation and typically require several days to complete the chemical sample analysis.